Islands of Ireland: Only sheep or local boatmen have easy access to Kerry's Two-Headed Island

It's named for its shape rather than any two-headed sea monsters 

Islands of Ireland: Two Headed Island, Kerry is in Derrynane Bay on the Iveragh Peninsula 

Though it is tempting to imagine that this County Kerry island was named after some ferocious creature from the deep such as the mythological Kraken, the answer is much more prosaic. Its name derives (in Irish Oileán Dá Cheann) from its double morphology which gives it the appearance of two heads.

As with Long Island in Roaringwater Bay, West Cork, Two-Headed Island is so named for its appearance, though in scrutinising this island from up close and distantly from Coomakista Pass on the Iveragh Peninsula, Two-Bodied Island might have been more appropriate.